Multi-Functional and Non-Acidic Iron Sulfide Scale Dissolver for Downhole Applications

Abstract

Abstract Iron sulfide scale is one of the major flow assurance issues for the oil and gas fields. Mechanical descaling is currently applied, but it is time consuming and costly. Dissolvers based on concentrated hydrochloric (HCl) acid have high dissolving power, but they also have limited applicability due to overwhelming drawbacks such as corrosion and H2S generation. This paper presents the latest development of alternative iron sulfide scale dissolvers for downhole applications. The selection criteria of alternative iron sulfide scale dissolver are high dissolution performance, low corrosion to carbon steel at elevated temperature, no H2S evolution and no formation damage. Three typical conventional iron sulfide scale dissolvers (THPS, pH neutralized chelate, and traditional chelate), along with 15wt% HCl were used as reference to compare the performance of the newly developed dissolver. Static dissolution tests and general and localized corrosion tests at elevated temperature were carried out to evaluate the dissolution and corrosion performance. Dynamic core flood tests were performed to investigate the potential formation permeability alteration when the chemical enters into the formation near wellbore, and CT scan was conducted to investigate the effect of dissolver on reservoir stimulation. Test results indicate that the new non-acidic iron sulfide scale dissolver is an efficient and cost effective alternative for removing iron sulfide dominated scale deposited in downhole tubular and near wellbore. Results showed the new developed dissolver performed significantly better performance in term of iron sulfide dissolution capacity and much lower corrosion at high temperature. In addition, this new dissolver has no H2S generation and iron sulfide re-precipitation problems, which is significantly improve the efficient and safe operations. Moreover, it showed multifunctional characteristic of well stimulation, addressed and confirmed by dynamic coreflood evaluation and CT scan. The new developed iron sulfide dissolver can mitigate iron sulfide deposited in tubing, near wellbore, and topside facilities with issues of iron sulfide black powder and schmoo.